struct.go

Documentation: archive/zip

  // Copyright 2010 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  /*
  Package zip provides support for reading and writing ZIP archives.
  
  See: https://www.pkware.com/appnote
  
  This package does not support disk spanning.
  
  A note about ZIP64:
  
  To be backwards compatible the FileHeader has both 32 and 64 bit Size
  fields. The 64 bit fields will always contain the correct value and
  for normal archives both fields will be the same. For files requiring
  the ZIP64 format the 32 bit fields will be 0xffffffff and the 64 bit
  fields must be used instead.
  */
  package zip
  
  import (
  	"os"
  	"path"
  	"time"
  )
  
  // Compression methods.
  const (
  	Store   uint16 = 0 // no compression
  	Deflate uint16 = 8 // DEFLATE compressed
  )
  
  const (
  	fileHeaderSignature      = 0x04034b50
  	directoryHeaderSignature = 0x02014b50
  	directoryEndSignature    = 0x06054b50
  	directory64LocSignature  = 0x07064b50
  	directory64EndSignature  = 0x06064b50
  	dataDescriptorSignature  = 0x08074b50 // de-facto standard; required by OS X Finder
  	fileHeaderLen            = 30         // + filename + extra
  	directoryHeaderLen       = 46         // + filename + extra + comment
  	directoryEndLen          = 22         // + comment
  	dataDescriptorLen        = 16         // four uint32: descriptor signature, crc32, compressed size, size
  	dataDescriptor64Len      = 24         // descriptor with 8 byte sizes
  	directory64LocLen        = 20         //
  	directory64EndLen        = 56         // + extra
  
  	// Constants for the first byte in CreatorVersion.
  	creatorFAT    = 0
  	creatorUnix   = 3
  	creatorNTFS   = 11
  	creatorVFAT   = 14
  	creatorMacOSX = 19
  
  	// Version numbers.
  	zipVersion20 = 20 // 2.0
  	zipVersion45 = 45 // 4.5 (reads and writes zip64 archives)
  
  	// Limits for non zip64 files.
  	uint16max = (1 << 16) - 1
  	uint32max = (1 << 32) - 1
  
  	// Extra header IDs.
  	//
  	// IDs 0..31 are reserved for official use by PKWARE.
  	// IDs above that range are defined by third-party vendors.
  	// Since ZIP lacked high precision timestamps (nor a official specification
  	// of the timezone used for the date fields), many competing extra fields
  	// have been invented. Pervasive use effectively makes them "official".
  	//
  	// See http://mdfs.net/Docs/Comp/Archiving/Zip/ExtraField
  	zip64ExtraID       = 0x0001 // Zip64 extended information
  	ntfsExtraID        = 0x000a // NTFS
  	unixExtraID        = 0x000d // UNIX
  	extTimeExtraID     = 0x5455 // Extended timestamp
  	infoZipUnixExtraID = 0x5855 // Info-ZIP Unix extension
  )
  
  // FileHeader describes a file within a zip file.
  // See the zip spec for details.
  type FileHeader struct {
  	// Name is the name of the file.
  	// It must be a relative path, not start with a drive letter (e.g. C:),
  	// and must use forward slashes instead of back slashes.
  	Name string
  
  	// Comment is any arbitrary user-defined string shorter than 64KiB.
  	Comment string
  
  	// NonUTF8 indicates that Name and Comment are not encoded in UTF-8.
  	//
  	// By specification, the only other encoding permitted should be CP-437,
  	// but historically many ZIP readers interpret Name and Comment as whatever
  	// the system's local character encoding happens to be.
  	//
  	// This flag should only be set if the user intends to encode a non-portable
  	// ZIP file for a specific localized region. Otherwise, the Writer
  	// automatically sets the ZIP format's UTF-8 flag for valid UTF-8 strings.
  	NonUTF8 bool
  
  	CreatorVersion uint16
  	ReaderVersion  uint16
  	Flags          uint16
  
  	// Method is the compression method. If zero, Store is used.
  	Method uint16
  
  	// Modified is the modified time of the file.
  	//
  	// When reading, an extended timestamp is preferred over the legacy MS-DOS
  	// date field, and the offset between the times is used as the timezone.
  	// If only the MS-DOS date is present, the timezone is assumed to be UTC.
  	//
  	// When writing, an extended timestamp (which is timezone-agnostic) is
  	// always emitted. The legacy MS-DOS date field is encoded according to the
  	// location of the Modified time.
  	Modified     time.Time
  	ModifiedTime uint16 // Deprecated: Legacy MS-DOS date; use Modified instead.
  	ModifiedDate uint16 // Deprecated: Legacy MS-DOS time; use Modified instead.
  
  	CRC32              uint32
  	CompressedSize     uint32 // Deprecated: Use CompressedSize64 instead.
  	UncompressedSize   uint32 // Deprecated: Use UncompressedSize64 instead.
  	CompressedSize64   uint64
  	UncompressedSize64 uint64
  	Extra              []byte
  	ExternalAttrs      uint32 // Meaning depends on CreatorVersion
  }
  
  // FileInfo returns an os.FileInfo for the FileHeader.
  func (h *FileHeader) FileInfo() os.FileInfo {
  	return headerFileInfo{h}
  }
  
  // headerFileInfo implements os.FileInfo.
  type headerFileInfo struct {
  	fh *FileHeader
  }
  
  func (fi headerFileInfo) Name() string { return path.Base(fi.fh.Name) }
  func (fi headerFileInfo) Size() int64 {
  	if fi.fh.UncompressedSize64 > 0 {
  		return int64(fi.fh.UncompressedSize64)
  	}
  	return int64(fi.fh.UncompressedSize)
  }
  func (fi headerFileInfo) IsDir() bool        { return fi.Mode().IsDir() }
  func (fi headerFileInfo) ModTime() time.Time { return fi.fh.ModTime() }
  func (fi headerFileInfo) Mode() os.FileMode  { return fi.fh.Mode() }
  func (fi headerFileInfo) Sys() interface{}   { return fi.fh }
  
  // FileInfoHeader creates a partially-populated FileHeader from an
  // os.FileInfo.
  // Because os.FileInfo's Name method returns only the base name of
  // the file it describes, it may be necessary to modify the Name field
  // of the returned header to provide the full path name of the file.
  // If compression is desired, callers should set the FileHeader.Method
  // field; it is unset by default.
  func FileInfoHeader(fi os.FileInfo) (*FileHeader, error) {
  	size := fi.Size()
  	fh := &FileHeader{
  		Name:               fi.Name(),
  		UncompressedSize64: uint64(size),
  	}
  	fh.SetModTime(fi.ModTime())
  	fh.SetMode(fi.Mode())
  	if fh.UncompressedSize64 > uint32max {
  		fh.UncompressedSize = uint32max
  	} else {
  		fh.UncompressedSize = uint32(fh.UncompressedSize64)
  	}
  	return fh, nil
  }
  
  type directoryEnd struct {
  	diskNbr            uint32 // unused
  	dirDiskNbr         uint32 // unused
  	dirRecordsThisDisk uint64 // unused
  	directoryRecords   uint64
  	directorySize      uint64
  	directoryOffset    uint64 // relative to file
  	commentLen         uint16
  	comment            string
  }
  
  // timeZone returns a *time.Location based on the provided offset.
  // If the offset is non-sensible, then this uses an offset of zero.
  func timeZone(offset time.Duration) *time.Location {
  	const (
  		minOffset   = -12 * time.Hour  // E.g., Baker island at -12:00
  		maxOffset   = +14 * time.Hour  // E.g., Line island at +14:00
  		offsetAlias = 15 * time.Minute // E.g., Nepal at +5:45
  	)
  	offset = offset.Round(offsetAlias)
  	if offset < minOffset || maxOffset < offset {
  		offset = 0
  	}
  	return time.FixedZone("", int(offset/time.Second))
  }
  
  // msDosTimeToTime converts an MS-DOS date and time into a time.Time.
  // The resolution is 2s.
  // See: http://msdn.microsoft.com/en-us/library/ms724247(v=VS.85).aspx
  func msDosTimeToTime(dosDate, dosTime uint16) time.Time {
  	return time.Date(
  		// date bits 0-4: day of month; 5-8: month; 9-15: years since 1980
  		int(dosDate>>9+1980),
  		time.Month(dosDate>>5&0xf),
  		int(dosDate&0x1f),
  
  		// time bits 0-4: second/2; 5-10: minute; 11-15: hour
  		int(dosTime>>11),
  		int(dosTime>>5&0x3f),
  		int(dosTime&0x1f*2),
  		0, // nanoseconds
  
  		time.UTC,
  	)
  }
  
  // timeToMsDosTime converts a time.Time to an MS-DOS date and time.
  // The resolution is 2s.
  // See: http://msdn.microsoft.com/en-us/library/ms724274(v=VS.85).aspx
  func timeToMsDosTime(t time.Time) (fDate uint16, fTime uint16) {
  	fDate = uint16(t.Day() + int(t.Month())<<5 + (t.Year()-1980)<<9)
  	fTime = uint16(t.Second()/2 + t.Minute()<<5 + t.Hour()<<11)
  	return
  }
  
  // ModTime returns the modification time in UTC using the legacy
  // ModifiedDate and ModifiedTime fields.
  //
  // Deprecated: Use Modified instead.
  func (h *FileHeader) ModTime() time.Time {
  	return msDosTimeToTime(h.ModifiedDate, h.ModifiedTime)
  }
  
  // SetModTime sets the Modified, ModifiedTime, and ModifiedDate fields
  // to the given time in UTC.
  //
  // Deprecated: Use Modified instead.
  func (h *FileHeader) SetModTime(t time.Time) {
  	t = t.UTC() // Convert to UTC for compatibility
  	h.Modified = t
  	h.ModifiedDate, h.ModifiedTime = timeToMsDosTime(t)
  }
  
  const (
  	// Unix constants. The specification doesn't mention them,
  	// but these seem to be the values agreed on by tools.
  	s_IFMT   = 0xf000
  	s_IFSOCK = 0xc000
  	s_IFLNK  = 0xa000
  	s_IFREG  = 0x8000
  	s_IFBLK  = 0x6000
  	s_IFDIR  = 0x4000
  	s_IFCHR  = 0x2000
  	s_IFIFO  = 0x1000
  	s_ISUID  = 0x800
  	s_ISGID  = 0x400
  	s_ISVTX  = 0x200
  
  	msdosDir      = 0x10
  	msdosReadOnly = 0x01
  )
  
  // Mode returns the permission and mode bits for the FileHeader.
  func (h *FileHeader) Mode() (mode os.FileMode) {
  	switch h.CreatorVersion >> 8 {
  	case creatorUnix, creatorMacOSX:
  		mode = unixModeToFileMode(h.ExternalAttrs >> 16)
  	case creatorNTFS, creatorVFAT, creatorFAT:
  		mode = msdosModeToFileMode(h.ExternalAttrs)
  	}
  	if len(h.Name) > 0 && h.Name[len(h.Name)-1] == '/' {
  		mode |= os.ModeDir
  	}
  	return mode
  }
  
  // SetMode changes the permission and mode bits for the FileHeader.
  func (h *FileHeader) SetMode(mode os.FileMode) {
  	h.CreatorVersion = h.CreatorVersion&0xff | creatorUnix<<8
  	h.ExternalAttrs = fileModeToUnixMode(mode) << 16
  
  	// set MSDOS attributes too, as the original zip does.
  	if mode&os.ModeDir != 0 {
  		h.ExternalAttrs |= msdosDir
  	}
  	if mode&0200 == 0 {
  		h.ExternalAttrs |= msdosReadOnly
  	}
  }
  
  // isZip64 reports whether the file size exceeds the 32 bit limit
  func (fh *FileHeader) isZip64() bool {
  	return fh.CompressedSize64 >= uint32max || fh.UncompressedSize64 >= uint32max
  }
  
  func msdosModeToFileMode(m uint32) (mode os.FileMode) {
  	if m&msdosDir != 0 {
  		mode = os.ModeDir | 0777
  	} else {
  		mode = 0666
  	}
  	if m&msdosReadOnly != 0 {
  		mode &^= 0222
  	}
  	return mode
  }
  
  func fileModeToUnixMode(mode os.FileMode) uint32 {
  	var m uint32
  	switch mode & os.ModeType {
  	default:
  		m = s_IFREG
  	case os.ModeDir:
  		m = s_IFDIR
  	case os.ModeSymlink:
  		m = s_IFLNK
  	case os.ModeNamedPipe:
  		m = s_IFIFO
  	case os.ModeSocket:
  		m = s_IFSOCK
  	case os.ModeDevice:
  		if mode&os.ModeCharDevice != 0 {
  			m = s_IFCHR
  		} else {
  			m = s_IFBLK
  		}
  	}
  	if mode&os.ModeSetuid != 0 {
  		m |= s_ISUID
  	}
  	if mode&os.ModeSetgid != 0 {
  		m |= s_ISGID
  	}
  	if mode&os.ModeSticky != 0 {
  		m |= s_ISVTX
  	}
  	return m | uint32(mode&0777)
  }
  
  func unixModeToFileMode(m uint32) os.FileMode {
  	mode := os.FileMode(m & 0777)
  	switch m & s_IFMT {
  	case s_IFBLK:
  		mode |= os.ModeDevice
  	case s_IFCHR:
  		mode |= os.ModeDevice | os.ModeCharDevice
  	case s_IFDIR:
  		mode |= os.ModeDir
  	case s_IFIFO:
  		mode |= os.ModeNamedPipe
  	case s_IFLNK:
  		mode |= os.ModeSymlink
  	case s_IFREG:
  		// nothing to do
  	case s_IFSOCK:
  		mode |= os.ModeSocket
  	}
  	if m&s_ISGID != 0 {
  		mode |= os.ModeSetgid
  	}
  	if m&s_ISUID != 0 {
  		mode |= os.ModeSetuid
  	}
  	if m&s_ISVTX != 0 {
  		mode |= os.ModeSticky
  	}
  	return mode
  }
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